High-strength lightweight tufted backing and method for the production thereof

ABSTRACT

The invention relates to a high-strength lightweight tufted backing, particularly for use as primary or secondary carpet backing, comprising at least one ply of melt-spun synthetic filaments, which are bonded by means of high-energy water jets, characterized in that it includes a small amount of a thermally activatable binding agent, which is applied onto the ply of melt-spun filaments in the form of at least one thin layer.

TECHNICAL FIELD

The invention relates to a high-strength lightweight tufted backing made of spunbonded non-woven, which comprises at least one ply of melt-spun synthetic filaments, which are bonded by means of high-energy water jets.

STATE OF THE ART

From the printed German patent specification DE 17 60 811, a tufted backing based on a spunbonded non-woven fabric made of polypropylene is known. The filaments forming this tufted backing have a rough individual titer of more than 10 dtex and are drawn in segments in a special manner such that drawn longer segments having high crystallinity in the same thread are followed by less drawn, less crystalline segments having a slightly lower melting temperature. These are used in the composite as the binding component, which is activated during the subsequent thermal bonding using direct vapor. According to the patent literature, the length of the well-drawn crystalline segment is approximately 11 inches, and the length of the subsequent less drawn and less crystalline segment is approximately 1 inch. The weight proportion of the low-crystalline segments is consequently slightly higher than 8%. The special non-woven structure of such a tufted backing is rather unimportant for this analysis.

From the printed German patent specifications DE 22 40 437 and DE 24 48 299, tufted backings based on a spunbonded non-woven fabric made of polyester are known. Also according to these patents, coarse threads are used for producing the tufted backing, which is to say matrix threads made of polyethylene terephthalate having a titer of more than 10 dtex. According to the published prior art, simultaneously with the matrix threads made of polyethylene terephthalate also binding threads having a lower titer and made of a low-melting copolyester are spun. The weight proportion of these binding threads is approximately 20%.

According to the teachings of the above-mentioned patents, a tufted backing should be configured such that in the system comprising matrix threads and bonds the bonds between the threads are always weaker than the threads bound by them. In this way, it can be achieved that a tufted backing in the basic state has sufficiently high strength. In the subsequent tufting process, in which a large number of needles penetrates the backing and sews it into the pile yarn, primarily the bonds between the threads are broken, without resulting in thread breakages. The threads can give way to the penetrating needles and form a “collar” around the tufted-in pile yarn. In this way, the strength and the resistance to tear propagation of the tufted base carpet are maintained at a high level, and hardly any damage is produced by the tufting process.

With the known thermally bonded systems it has been found that the bonds generally have very high strength and that targeted influencing of the binding strength is very difficult. In order to adjust the above-described relation between the bond strength and thread strength, therefore the only remaining possibility is to increase the thread strength by using coarser threads. Consequently, in the above-mentioned art titers of more than 10 dtex are proposed for the matrix threads. A considerable disadvantage of such coarse threads, however, is that high basis weights in the magnitude of at least 100 to 120 g/m² are required in order to achieve the strength and coverage sufficient for tufted backings.

In order to overcome this disadvantage, it is proposed in the printed German patent specification DE 198 21 848 C2, which forms the generic prior art, to produce a tufted backing from a spunbonded non-woven made of synthetic filaments without binding agent, wherein the spunbonded non-woven is to be bonded only by the action of high-energy water jets. During the interlacing of the filaments by water jets, a plurality of very weak bonds are produced. Each such bond based solely on interfacial friction is very weak per se—in any case weaker than the filaments interlaced in this way. The bonds can consequently be loosened, without the filaments being damaged or even broken, whereby the mobility of the filaments in the tufting process is unreservedly ensured. No significant damage occurs to the filament structure during tufting. On the other hand, however, the very high number of weak bonds adds up to such an extent that the non-woven fabric bonded in this way overall has quite high absolute strength. A significant advantage of this system is that for the design of the non-woven fabric finer filaments may be used. The patent specification states titers of 0.7 to 6 dtex. In this way, it is possible to produce spunbonded non-wovens having lower basis weights, having both sufficient strength and also appearing cohesive enough to be used as tufted backings.

The disadvantage of the above-mentioned tufted backing is that while it does not lose strength as a result of the tufting process, the initial modulus of the base carpet is low, thereby making the carpet not sufficiently dimensionally stable for the further processing steps.

The almost inevitable stresses occurring during the refining steps may in particular result in longitudinal deformation, and associated therewith lateral contraction of the base carpet. In order to prevent this, corresponding precautionary measures, such as tension control, must be taken.

DESCRIPTION OF THE INVENTION

It is an object of the invention to refine a tufted backing of the generic type such that it has sufficient strength and therefore dimensional stability for further processing even after tufting, without impairing the known good behavior during tufting.

This object is achieved by a tufted backing having all the characteristics of claim 1. A method for producing a tufted backing according to the invention is described in claim 11, and a preferred use of the invention is described in claim 15. Preferred embodiments of the invention are described in the dependent claims.

According to the invention, it is provided for a high-strength lightweight tufted backing made of spunbonded non-woven, having at least one ply of melt-spun synthetic filaments bonded by means of high-energy water jets, that this backing comprises a small amount of a thermally activatable binding agent, which is applied onto the ply of melt-spun filaments in the form of at least one thin layer.

Without thereby limiting the invention, it is presumed that the tufting process may result in excessive loosening of the weak bonds in the backing. Apparently, this reduces the initial modulus of the base carpet so much that the base carpet during further processing is not sufficiently dimensionally stable. The result is the described deformation of the base carpet.

Surprisingly it was found that by applying at least one thin layer of a binding agent onto the ply of melt-spun synthetic filaments, together with the subsequent hydroentangling, drying, and activation of the binding agent, further bonds (or bonding sites)—in addition to the water jet bonds—are created between the spun-bonded non-woven filaments, said bonds still being weak enough to apparently not impair the mobility of the spunbonded non-woven filaments during tufting. The high number, remaining after tufting, of fine spun-bonded non-woven filaments bonded to each other by the above-mentioned additional bonding sites contributes to the fact that the carpet has high modulus values and a dimensional stability that is sufficient for further processing. With the tufted backing according to the invention no further measures for dimensional stabilization, such as the above-mentioned tension control, are required during further processing. It is suspected that this effect, among other things, can also be attributed to the fact that part of the binding agent is also carried down into the deeper layers of the non-woven fabric ply by the high-energy water jets and forms bonding sites there.

A tufted backing according to the invention may be composed of one, or also several plies of spunbonded non-woven and binding agent. Other additional plies may also be provided, to the extent they neither interfere with the tufting process nor with further processing.

In a preferred embodiment of the invention, the tufted backing according to the invention has a 3-ply structure, in which the middle ply comprises the binding agent and the outer plies the melt-spun synthetic filaments. Because hydroentangling is frequently carried out on both sides, this has the advantage that the binding agent is introduced into the non-woven fabric ply both from beneath and above.

In particular low-melting thermoplastic polymers are suited as binding agents, wherein such thermoplastic polymers are preferred, the melting temperatures of which are sufficiently lower than those of the spun-bonded non-woven filaments. The melting temperature should preferably be at least 10° C., in a particularly preferred embodiment at least 20° C. below the melting temperature of the spun-bonded non-woven filaments, so that they are not damaged during the thermal activation.

In a preferred embodiment, the low-melting thermoplastic polymers also have a broad softening range. This has the advantage that the thermoplastic polymer used as the binding agent can be activated at lower temperatures than the effective melting point thereof. From a technological point of view, the binding agent does not necessarily have to be fully melted, but instead it suffices that it is sufficiently softened, thereby adhering to the filaments to be bound. In this way, during the activation phase the binding degree between the spun-bonded non-woven filaments and the binding agent can be adjusted.

The low-melting thermoplastic polymer preferably substantially comprises a polyethylene, a copolymer having a substantial proportion of polyethylene, polypropylene, a copolymer having a substantial proportion of polypropylene, a copolyester, a polyamide and/or a copolyamide.

The weight proportion of the low-melting polymer, relative to the total weight of the tufted backing, should not exceed 7%. If the proportion of the hot-melt adhesive is too high, the risk arises that the spunbonded non-woven fabric is thermally bonded too strongly. In any case, the bonds produced by the hot-melt adhesive would be stronger than those produced by the bound filament. During the tufting process, the filaments would then become significantly damaged and torn, and therefore the strength after tufting, in particular also the resistance to tear propagation, would be excessively impaired.

The weight proportion is preferably between 1.5 and 5% by weight. With a weight proportion of less than 1.5% by weight, the reinforcement effect, in particular also with respect to the initial modulus, would not be sufficiently pronounced. In addition, due to the low quantity, also no sufficiently good distribution of the binding agent in the spunbonded non-woven cross-section would be achieved by the water jet treatment. However, even the use of smaller proportions of hot-melt adhesive are advantageous and should therefore be encompassed by the present invention.

The low-melting polymer can be present, for example, in the form of fibers or fibrils. In particular conjugate fibers can be used as the fibers, wherein the lower-melting component constitutes the thermally activatable binding agent.

The present invention enables the use of filaments having a low titer for the spun-bonded non-woven filaments. Even with low basis weights, good strength and sufficient coverage is achieved. The fiber titer preferably ranges between 0.7 and 6 dtex. Fibers having a titer between 1 and 4 dtex have the special advantage that they ensure good surface coverage with average basis weights, however still have sufficient overall strength so that they are not damaged or torn during the tufting process by the penetration of the needles.

A tufted backing according to the invention preferably includes filaments comprising polyester, particularly polyethylene terephthalate, and/or polyolefin, particularly polypropylene. These materials are particularly suited because they are produced from mass raw materials, which are available anywhere in sufficient quantities and sufficient quality. Both polyester and polypropylene are well-known in the production of fibers and non-woven fabrics for the durability thereof.

A suitable method for producing a tufted backing according to the invention comprises the following steps:

-   -   a) Depositing at least one ply of synthetic filaments by means         of a spun-bonded non-woven production process;     -   b) applying at least one thin layer of a thermally activatable         binding agent;     -   c) distributing the binding agent and bonding the spun-bonded         non-woven filaments by means of high-energy high-pressure water         jets;     -   d) drying     -   e) thermal treatment in order to activate the binding agent.

The production of spunbonded non-wovens, which is to say the spinning of synthetic filaments from different polymers, including polypropylene or polyester, and also the deposition thereof to form a random non-woven on a backing are state of the art. Large machines having widths of 5 m and more can be purchased from several companies. They can have one or more spinning systems (spin-die manifolds) and be adjusted to the desired output. Hydroentangling systems are also state of the art. Such machines as well can be provided by several manufacturers in large widths. The same applies to dryers and winders.

The thermally activatable binding agent can be applied by different methods, such as by powder application, or also in the form of a dispersion. The binding agent, however, is preferably applied in the form of fibers or fibrils using a melt-blown or air-laying method. These methods too are known and described in many places in literature.

Melt-blown and air-laying methods have the particular advantage that they can be arbitrarily combined with spinning systems for the spunbonded non-woven filaments.

As is known from DE 198 21 848 C2, hydroentangling should preferably be carried out such that a specific longitudinal strength of at least 4.3 N/5 cm per g/m² of the surface mass and an initial modulus, measured in the longitudinal direction as tension for 5% elongation, of at least 0.45 N/5 cm per g/m² surface mass can be achieved. In this way, sufficient strength of the tufted backing and sufficiently good distribution of the binding agent in the spunbonded non-woven ply are ensured.

Activation as defined by the invention shall denote the creation of bonding sites using the binding agent, for example by melting a low-melting polymer used as the binding agent for deposition or adherence. Both the drying operation and the thermal treatment for activation are to be carried out at temperatures that are so low that damage to the spunbonded non-woven filaments, for example as a result of melting for deposition or adherence, is safely avoided. For economical reasons with respect to the method, the drying operation and the thermal activation of the binding agent are preferably carried out in one step. In order to dry and activate the low-melting polymer, different types of dryers may be used, such as tenters, belt driers, or surface driers, preferably however a drum dryer is suited. During the end phase, the drying temperature should preferably be approximately adjusted to the melting temperature of the low-melting polymer and optimized as a function of the results. Here, particularly the entire melting behavior of the binding agent must be taken into account. When using one that has a pronounced wide softening range, it is not necessary to aim for the physical melting point. Rather, it suffices to look for the optimization of the binding effect already in the softening range. In this way, unpleasant marginal effects, such as adhesion of the binding component to machine parts and over-bonding, can be avoided.

The tufted backing according to the invention is not only suited as primary, but also as secondary carpet backing. Due to the excellent mechanical properties thereof, a tufted backing according to the invention is in particular also suited for producing a three-dimensionally deformable carpet, in particular for automotive interior applications.

The invention will be explained in more detail hereafter based on the exemplary embodiments:

EXAMPLE 1

The test machine for the production of spunbonded non-wovens had a width of 1200 mm. It included a spinneret, which extended across the entire width of the machine, two mutually opposed blow walls disposed parallel to the spinneret, and an extraction gap connecting thereto, which in the lower region expanded into a diffuser and formed a non-woven forming chamber. The spun filaments formed a uniform fabric, which is to say a spunbonded non-woven, on a collection belt suctioned downwardly in the non-woven forming region. Said non-woven was pressed together between two rolls and rolled up.

The pre-bonded spunbonded non-woven was unrolled on a test machine for hydroentangling. With the help of an air-laying system, on the surface thereof a thin layer of short bonding fibers was applied, and the two-layer textile was subsequently treated with a plurality of high-energy water jets, thereby hydroentangled and bonded. At the same time, the binding agent was distributed in the textile. Thereafter, the bonded multi-layer non-woven was dried in a drum dryer, wherein in the end zone of the dryer the temperature was adjusted such that the bonding fibers were activated and brought about additional binding.

In this experiment, a spunbonded non-woven was produced from polypropylene. A spinneret was used, which had 5479 spinning holes across the width described above. The raw material used was polypropylene granules from Exxon Mobile (Achieve PP3155), having an MFI of 36. The spinning temperature was 272° C. The extraction gap had a width of 25 mm. The filament titer was 2.1 dtex, measured based on the diameter in the spunbonded non-woven. The production speed was adjusted to 41 m/min. The resulting spunbonded non-woven had a basis weight of 78 g/m². On the hydroentangling machine, first a layer of 3 g/m² comprising very short conjugate fibers in a shell/core configuration was applied with the aid of a device for non-woven formation under an air current, wherein the core was made of polypropylene and the shell of polyethylene. The weight ratio of the components was 50/50%. Thereafter, the spunbonded non-woven was subjected to the hydroentangling step. The bonding was carried out with the help of 6 manifolds, with alternately acted upon both sides.

The water pressure used in each case was adjusted as follows:

Manifold no. 1 2 3 4 5 6 Water pressure (bar) 20 50 50 50 150 150

During the hydroentangling step, the short fibers were largely drawn into the spunbonded non-woven, so that they did not form a true surface layer.

Thereafter, the spunbonded non-woven treated with water jets was dried in a drum dryer. In the last zone, the air temperature was adjusted to 123° C., so that the polyethylene melted easily and formed thermal bonds. The spunbonded non-woven bonded in this way had the following mechanical values for a basis weight of 80 g/m²:

Maximum Maximum tensile Force at 5% Force at 10% tensile force elongation elongation elongation [N/5 cm] [%] [N/5 cm] [N/5 cm] longitudinal 396 85 45 75 transverse 70 105 4.5 9.8

The specific strength in the longitudinal direction was 4.95 N/5 cm per g/m² and the specific secant modulus at 5% elongation was 0.56 N/5cm per g/m².

The bonded spunbonded non-woven was easy to tuft with conventional machine gauges. A machine gauge of 1/64 inch resulted in the tufted state in the following mechanical values:

Maximum Maximum tensile Tear propagation tensile force elongation force [N/5 cm] [N/5 cm] [N] longitudinal 460 85 220 transverse 110 100 ./.

EXAMPLE 2

Polyester granules were used on the same test machine as described in Example 1. These granules had an intrinsic viscosity of IV=0.67. They were thoroughly dried, so that the residual water content was below 0.01% and spinning was carried out at a temperature of 285° C. In the process, as in Example 1, a spinneret having 5479 holes across a width of 1200 mm was used. The polymer throughput was 320 kg/h. In the spunbonded non-woven, the filaments had a visually determined titer of 2 dtex and very low shrinkage. The machine speed was adjusted to 55 m/min, so that the pre-bonded spunbonded non-woven had a basis weight of 80 g/m².

The non-woven was placed in the same machine for hydroentangling. A layer of 3 g/m² of the same short conjugate fibers (PP/PE 50/50) was placed on the surface of the pre-bonded spunbonded non-woven. Thereafter, the multi-layer material ran through the hydroentangling step using 6 manifolds, which were adjusted as follows:

Manifold no. 1 2 3 4 5 6 Water pressure (bar) 20 50 80 80 200 200

During the hydroentangling step, the short bonding fibers were largely drawn into the spunbonded non-woven, so that they did not form a true surface layer.

Thereafter, the spunbonded non-woven treated with water jets was dried in a drum dryer. In the last zone, the air temperature was adjusted to 123° C., so that the polyethylene melted easily and formed thermal bonds. The spunbonded non-woven bonded in this way had the following mechanical values for a basis weight of 82 g/m²:

Maximum Maximum tensile Force at 5% Force at 10% tensile force elongation elongation elongation [N/5 cm] [%] [N/5 cm] [N/5 cm] longitudinal 395 88 48 80 transverse 75 100 4.9 10.2

The specific strength in the longitudinal direction was 4.82 N/5 cm per g/m² and the specific secant modulus at 5% elongation was 0.59 N/5 cm per g/m².

The bonded spunbonded non-woven was easy to tuft with different gauges. A machine setting of 1/64 inch resulted in the tufted state in the following mechanical values:

Maximum Maximum tensile Tear propagation tensile force elongation force [N/5 cm] [N/5 cm] [N] longitudinal 468 80 225 transverse 120 95 ./.

During additional operations, the behavior of the tufted carpet was referred to as stable. 

1. A high-strength lightweight tufted backing made of spunbonded non-woven, particularly for use as primary or secondary carpet backing, comprising at least one ply of melt-spun synthetic filaments bonded by means of high-energy water jets, wherein said at least one ply includes a small amount of a thermally activatable binding agent, which is applied onto the ply of melt-spun filaments in the form of at least one thin layer.
 2. The high-strength lightweight tufted backing according to claim 1, wherein said backing is configured as a 3-ply system, in which the middle ply comprises the binding agent and the two outer plies comprise synthetic filaments.
 3. The high-strength lightweight tufted backing according to claim 1, wherein the binding agent comprises a low-melting thermoplastic polymer.
 4. The high-strength lightweight tufted backing according to claim 3, wherein the low-melting thermoplastic polymer has a melting temperature that is at least 10° C. below that of the synthetic filaments.
 5. A high-strength lightweight tufted backing according to claim 1, wherein the synthetic filaments have a titer of 0.7 to 6.0 dtex.
 6. A high-strength lightweight tufted backing according to claim 1, wherein the synthetic filaments comprise polyester, polyethylene terephthalate, and/or a polyolefin.
 7. A high-strength lightweight tufted backing according to claim 1, wherein the low-melting polymer substantially comprises polyethylene, a copolymer having a proportion of polyethylene, polypropylene, a copolymer having a proportion of polypropylene, a copolyester, a polyamide, and/or a copolyamide.
 8. A high-strength lightweight tufted backing according to claim 3, wherein the low-melting polymer constitutes a weight proportion of less than 7% relative to the total weight of the tufted backing.
 9. A high-strength lightweight tufted backing according to claim 3, wherein the low-melting polymer is present in the form of spun or melt-blown fibers or fibrils.
 10. The high-strength lightweight tufted backing according to claim 9, wherein the fibers are conjugate fibers, wherein the lower-melting component constitutes the thermally activatable binding agent.
 11. A method for producing a high-strength lightweight tufted backing according to claim 1, characterized by the following steps: a) depositing at least one ply of synthetic filaments by means of a spun-bonded non-woven production process; b) applying at least one thin layer of a thermally activatable binding agent. c) hydroentangling the spunbonded non-woven filaments and distributing the binding agent by means of high-energy high-pressure water jets; d) drying; and e) thermal treatment in order to activate the binding agent.
 12. The method according to claim 11, wherein the drying and the thermal activation are carried out in one step.
 13. The method according to claim 11, wherein the hydroentangling is adjusted such that a specific longitudinal strength of at least 4.3 N/5 cm per g/m² basis weight and a specific initial modulus, measured in the longitudinal direction as tension at 5% elongation, of at least 0.45 g/5 cm per g/m² basis weight are achieved.
 14. A method according to claim 11, wherein the thermally activatable binding agent is applied by employing an air-laying or melt-blown method.
 15. Use of a high-strength lightweight tufted backing according to claim 1 for producing three-dimensionally deformable carpets for automotive interior applications. 